Epidemiology of the group B streptococcus: maternal and nosocomial sources for infant acquisitions.

Repeated bacteriologic observations were made in 462 newborn infants and correlated with similar data from their mothers to evaluate the relative contributions of the birth canal and the hospital environment to acquisition of group B streptococci in the first few days of life. Fifty-eight percent of infants whose mothers were intrapartum carriers acquired streptococci in comparison with 12% of those whose mothers were noncarriers. Acquisitions from the birth canal were not influenced by the route of delivery or the time between membrane rupture and birth, but could be related to the quantity of streptococci in maternal cultures. Observations in ten cohorts of infants, including serotyping and bacteriophage susceptibility of group B isolates, demonstrated clear-cut streptococcal spread among infants in two cohorts. Infants appeared to harbor larger numbers of streptococci at more body sites following acquisition from the birth canal than after acquisition from the hospital environment.